Method for producing catalyst for use in production of unsaturated aldehyde and/or unsaturated carboxylic acid, and method for producing unsaturated aldehyde and/or unsaturated carboxylic acid

ABSTRACT

A catalyst for use in the production of an unsaturated aldehyde and/or an unsaturated carboxylic acid, the catalyst comparing (or, preferably, being composed of) a mixed oxide containing molybdenum, bismuth and iron, which has improved methanical strength, is produced by a method including the steps of (1) drying an aqueous solution or an aqueous slurry containing raw materials of the catalyst and then firstly calcining a dried product in a molecular oxygen-containing gas atmosphere to obtain a calcined product; (2) heating the calcined product obtained in Step (1) in the presence of a reducing material to obtain a reduced product having a mass loss of 0.05 to 6%; and (3) secondly calcining the reduced product obtained in Step (2) in a molecular oxygen-containing gas atmosphere.

This application is a divisional of application Ser. No. 12/467,079,filed on May 15, 2009 and issued as U.S. Pat. No. 8,252,714, whichclaims priority under 35 U.S.C. §119(a) to Patent Application No.2008-129200 filed in Japan on May 16, 2008, all of which are herebyexpressly incorporated by reference into the present application and forwhich priority is claimed under 35 U.S.C. §120.

FIELD OF THE INVENTION

The present invention relates to a method for producing a catalyst foruse in the production of an unsaturated aldehyde and/or an unsaturatedcarboxylic acid. The present invention also relates to a method forproducing an unsaturated aldehyde and/or an unsaturated carboxylic acidby using a catalyst prepared by the foregoing method.

DESCRIPTION OF PRIOR ART

A catalyst composed of a mixed oxide comprising molybdenum, bismuth andiron is effective as a catalyst to be used for producing acrolein and/oracrylic acid by a gas phase catalytic oxidation of propylene withmolecular oxygen, and also effective as a catalyst to be used forproducing methacrolein and/or methacrylic acid by a gas phase catalyticoxidation of isobutylene or tert-butyl alcohol with molecular oxygen. Itis known that such a catalyst is prepared generally by drying an aqueoussolution or an aqueous slurry containing catalyst components and thencalcining the dried product. In the use of this type of catalyst for theabove oxidation reactions, the catalyst is filled in the form of amolded catalyst or a supported catalyst in a fixed bed reactor. If thecatalyst has low mechanical strength, it tends to be broken when it isfilled in a reactor and, as a result, a pressure drop occurs in thereactor during the reaction. Therefore, such a catalyst is required tohave high mechanical strength.

To increase the mechanical strength of a catalyst, the compounding ofinorganic fiber in a catalyst during the preparation thereof is proposed(see JP-A-06-000381, JP-A-2002-273229 and JP-A-09-052053).

However, a catalyst prepared by the above method may not necessarilyhave satisfactory mechanical strength.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for producinga catalyst for use in the production of an unsaturated aldehyde and/oran unsaturated carboxylic acid, which catalyst comprises a mixed oxidecomprising molybdenum, bismuth and iron and has improved mechanicalstrength.

As the result of extensive studies by the present inventors, it has beenfound that the above object can be accomplished when a catalyst for usein the production of an unsaturated aldehyde and/or an unsaturatedcarboxylic acid, the catalyst comprising (or, preferably, being composedof) a mixed oxide containing molybdenum, bismuth and iron, is used whichis produced by a method comprising Step (1), (2) and (3) describedbelow.

Thus, the present invention provides a method for producing a catalystfor use in the production of an unsaturated aldehyde and/or anunsaturated carboxylic acid, the catalyst comprising (or, preferably,being composed of) a mixed oxide comprising molybdenum, bismuth andiron, said method comprising the steps of

(1) drying an aqueous solution or an aqueous slurry containing rawmaterials of the catalyst and then firstly calcining a dried product ina molecular oxygen-containing gas atmosphere to obtain a calcinedproduct;

(2) heating the calcined product obtained in Step (1) in the presence ofa reducing material to obtain a reduced product having a mass loss,represented by the following equation (I), of 0.05 to 6%;Mass loss(%)=[(Wa−Wb)/Wa]×100  (I)in which Wa is a weight of a calcined product before the reductiontreatment, and Wb is a weight of a reduced product after the reductiontreatment; and

(3) secondly calcining the reduced product obtained in Step (2) in amolecular oxygen-containing gas atmosphere.

Furthermore, the present invention provides a method for producing anunsaturated aldehyde and/or an unsaturated carboxylic acid comprisingthe steps of:

producing a catalyst by the method for the production of the catalystaccording to the present invention, and

a gas phase catalytic oxidation of at least one compound selected fromthe group consisting of propylene, isobutylene and tert-butyl alcoholwith molecular oxygen in the presence of the catalyst produced in theabove step.

The method of the present invention can provide a catalyst having bettermechanical strength for use in the production of an unsaturated aldehydeand/or an unsaturated carboxylic acid. Moreover, when the catalystproduced by the method of the present invention is used in theproduction of an unsaturated aldehyde and/or an unsaturated carboxylicacid, the breakage of the catalyst is well prevented during filling itin a reactor. As a result, it is possible to reduce the pressure dropduring the reaction and to catalytically oxidize a compound selectedfrom the group consisting of propylene, isobutylene and tert-butylalcohol stably with molecular oxygen in a vapor phase to produce anunsaturated aldehyde and/or an unsaturated carboxylic acid.

DETAILED DESCRIPTION ON THE INVENTION

The catalyst for use in the production of an unsaturated aldehyde and/oran unsaturated carboxylic acid according to the present inventioncomprises (or, preferably, is composed of) a mixed oxide comprisingmolybdenum, bismuth and iron as the essential elements. The mixed oxidemay optionally contain at least one element other than molybdenum,bismuth and iron. For example, the mixed oxide may preferably contain atlease one element selected from the group consisting of nickel, cobalt,potassium, rubidium, cesium and thallium.

A preferable example of such a mixed oxide is a compound represented bythe following formula (II):Mo_(a)Bi_(b)Fe_(c)A_(d)B_(e)C_(f)D_(g)O_(x)  (II)whereinMo, Bi and Fe represent molybdenum, bismuth and iron, respectively,A represents nickel and/or cobalt,B represents an element selected from the group consisting of manganese,zinc, calcium, magnesium, tin and lead,C represents an element selected from the group consisting ofphosphorus, boron, arsenic, tellurium, tungsten, antimony, silicon,aluminum, titanium, zirconium and cerium,D represents an element selected from the group consisting of potassium,rubidium, cesium and thallium,O represents oxygen,a, b, c, d, e, f and g satisfy the following relationships: 0≦b≦10,0≦c≦10, 1≦d≦10, 0≦e≦10, 0≦f≦10 and 0≦g≦2, when a is set equal to 12, andx is a value determined depending upon the oxidation states of the otherelements. For example, x may be determined by multiplying the valence ofeach element (except for oxygen) comprised in the mixed oxide with itscorresponding stoichiometric proportion within the mixed oxide, andadding up the multiplication products to form a sum, whereby the sumthus formed divided by 2 equals x. Accordingly, if the mixed oxide is,for example, Mo₁₂Bi₅Fe₄Co₁₀CsO_(x) and the valences of Mo, Bi, Fe, Coand Cs in this compound are VI, III, III, II and I, respectively, x canbe determined by the above method asx=[(12·6)+(3·5)+(3·4)+(2·10)+(1·1)]/2=60 (i.e., the mixed oxide wouldhave the formula Mo₁₂Bi₅Fe₄Co₁₀CsO₆₀).

Among the compounds represented by formula (II), those having thefollowing compositions (except for oxygen atoms) are preferably used:Mo₁₂Bi_(0.1-5)Fe_(0.5-5)Co₅₋₁₀Cs_(0.01-1)Mo₁₂Bi_(0.1-5)Fe_(0.5-5)Co₅₋₁₀Sb_(0.1-5)K_(0.01-1)Mo₁₂Bi_(0.1-5)Fe_(0.5-5)Ni₅₋₁₀Sb_(0.1-5)Si_(0.1-5)Tl_(0.01-1)

Hereinafter, a method for producing the catalyst according to thepresent invention is explained. An aqueous solution or an aqueous slurrycontaining raw materials of the catalyst is dried and then, the driedproduct is calcined firstly in a molecular oxygen-containing gasatmosphere [Step (1)]. As the raw materials of the catalyst, in general,compounds of the respective elements constituting the catalyst, such asoxides, nitrates, sulfates, carbonates, hydroxides, oxoacids andammonium salts thereof, and halides, are used in ratios such thatdesired atomic ratios of the elements are satisfied. For example,molybdenum trioxide, molybdic acid, ammonium paramolybdate and the likemay be used as a molybdenum compound. Bismuth oxide, bismuth nitrate,bismuth sulfate and the like may be used as a bismuth compound. Iron(III) nitrate, iron (III) sulfate, iron (III) chloride and the like maybe used as an iron compound. Cobalt nitrate, cobalt sulfate, cobaltchloride and the like may be used as a cobalt compound. Antimonytrioxide, antimony (III) chloride and the like may be used as anantimony compound. Cesium nitrate, cesium carbonate, cesium hydroxideand the like may be used as a cesium compound.

The aqueous solution or the aqueous slurry containing the raw materialsmay be prepared by mixing the raw materials with water. A mixingtemperature and an amount of water used may adequately be selected. Theaqueous solution or the aqueous slurry may be dried using a kneader, abox dryer, a drum-type through-air dryer, a spray dryer, a flush dryer,or the like.

The dried product obtained by the above drying step is firstly calcined(first calcination) in the molecular oxygen-containing gas atmosphere.The concentration of molecular oxygen in the molecular oxygen-containinggas is usually from 1 to 30% by volume, and preferably from 10 to 25% byvolume. Ambient air or pure oxygen is usually used as the source ofmolecular oxygen. Such a source is used as a molecular oxygen-containinggas, if necessary, after being diluted with nitrogen, carbon dioxide,water, helium, argon, or the like. A calcination temperature in thefirst calcination step is usually from 300 to 600° C., and preferablyfrom 400 to 550° C. A calcination time in the first calcination step isusually from 5 minutes to 40 hours, and preferably from 1 to 20 hours.

The calcined product resulting from the first calcination is subjectedto heat treatment in the presence of a reducing material [Step (2)] toobtain a reduced product having a mass loss of from 0.05 to 6% byweight. Such a treatment conducted in the presence of a reducingmaterial will hereinafter be referred simply as a “reduction treatment”.The mass loss is defined by the following equation (I):Mass loss(%)=[(Wa−Wb)/Wa]×100  (I)in which Wa is a weight of a calcined product before the reductiontreatment, and Wb is a weight of a reduced product after the reductiontreatment.

Examples of the reducing material include hydrogen, ammonia, carbonmonoxide, hydrocarbons, alcohols, aldehydes and amines. Optionally, twoor more of such reducing materials may be used. Preferably,hydrocarbons, alcohols, aldehydes and amines each have 1 to about 6carbon atoms. Examples of such hydrocarbons include saturated aliphatichydrocarbons such as methane, ethane, propane, n-butane and isobutane,unsaturated aliphatic hydrocarbons such as ethylene, propylene,α-butylene, β-butylene and isobutylene, and aromatic hydrocarbons suchas benzene. Examples of such alcohols include saturated aliphaticalcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol,n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol and tert-butylalcohol, unsaturated aliphatic alcohols such as allyl alcohol, crotylalcohol and methallyl alcohol, and aromatic alcohols such as phenol.Examples of such aldehydes include saturated aliphatic aldehydes such asformaldehyde, acetaldehyde, propionaldehyde, n-butylaldehyde andisobutylaldehyde, and unsaturated aliphatic aldehydes such as acrolein,crotonaldehyde and methacrolein. Examples of such amines includesaturated aliphatic amines such as methylamine, dimethylamine,trimethylamine, ethylamine, diethylamine and triethylamine, andunsaturated aliphatic amines such as allylamine and diallylamine, andaromatic amines such as aniline.

The reduction treatment is usually conducted by subjecting the calcinedproduct to heat treatment in an atmosphere of a gas containing thereducing material. The concentration of the reducing material in the gasis usually from 0.1 to 50% by volume, and preferably from 3 to 30% byvolume. The reducing material may be diluted with nitrogen, carbondioxide, water, helium, argon, or the like so that such a concentrationcould be achieved. Molecular oxygen may be present in the reducingatmosphere unless the effect of the reduction treatment is affected.Preferably, no molecular oxygen is present in the reducing atmosphere.

A temperature for the reduction treatment is usually from 200 to 600°C., and preferably from 300 to 500° C. The time of the reductiontreatment is usually from 5 minutes to 20 hours and preferably from 30minutes to 10 hours. It is preferable to conduct the reduction treatmentby placing the calcined product in a tubular or box-shaped container andkeeping the container ventilated with a gas containing the reducingmaterial. At this time, a gas discharged from the container may becirculated and reused, if necessary.

Accordingly, the reduced product having a mass loss, represented by theabove equation (I), of 0.05 to 6% by weight is obtained. The mass lossmay be attributed to the loss of lattice oxygen atoms from the calcinedproduct, which results in the formation of the reduced product.Therefore, the mass loss of the calcined product may be used as anindicator to monitor the progress of reduction. When the progress ofreduction is small, sufficient effects of the reduction may not beattained. When the calcined product is excessively reduced, heat isabruptly generated in the second calcination step carried out in amolecular oxygen-containing atmosphere, which will be explained below,so that the temperature control may become difficult. Therefore, themass loss of the calcined product after the reduction treatment ispreferably from 0.1 to 5% by weight.

In the reduction treatment, the reducing material itself, decompositionproducts derived from the reducing material or the like may remain inthe catalyst after the reduction treatment according to the type of thereducing material used, heat treatment conditions or the like. In such acase, the mass loss can be calculated by measuring the weight of theresidual material in the catalyst and then calculating the weight afterthe reduction treatment by subtracting the mass of the residual materialfrom the weight of the catalyst including the residual material. Atypical residual material is carbon and, therefore, the mass of theresidual material can be determined, for example, by total carbon (TC)analysis.

The reduced product resulting from the reduction treatment is secondlycalcined (second calcination) in a molecular oxygen-containing gasatmosphere [Step (3)]. The molecular oxygen concentration of the gas isusually from 1 to 30% by volume, and preferably from 10 to 25% byvolume. Ambient air or pure oxygen is usually used as the source ofmolecular oxygen. Such a source is used as a molecular oxygen-containinggas, if necessary, after being diluted with nitrogen, carbon dioxide,water, helium, argon, or the like. The calcination temperature in thesecond calcination step is usually from 200 to 600° C., and preferablyfrom 350 to 550° C. The calcination time in the second calcination stepis usually from 5 minutes to 20 hours, and preferably from 30 minutes to10 hours.

The catalyst produced by the method of the present invention is usuallymolded in a desired form before use. The catalyst may be molded in theform of a ring, a pellet, a sphere or the like by tabletting, extrusionmolding or the like. The catalyst components may be supported on acarrier, for example, silica, alumina, silicon carbide and siliconnitride. In the molding, for improving the mechanical strength of thecatalyst, inorganic fiber or the like, which is substantially inert tothe intended oxidation reaction, may be added as disclosed in, forexample, JP-A-09-052053.

The present invention can increase the mechanical strength of thecatalyst by performing the second calcination. Therefore, the catalystis preferably molded before the second calcination. Specifically, it ispreferable to mold the dried product obtained by drying the aqueoussolution or the aqueous slurry containing the raw materials of thecatalyst, the calcined product obtained by the first calcination, or thereduced product obtained by the reducing treatment.

Thus, the method of the present invention can improve the mechanicalstrength of a catalyst for use in the production of an unsaturatedaldehyde and/or an unsaturated carboxylic acid which catalyst comprises(or, preferably, is composed of) a mixed oxide comprising molybdenum,bismuth and iron. Accordingly, the breakage of the catalyst is preventedwhen it is filled in a reactor. As a result, it is possible to reducethe pressure drop during the reaction, to catalytically oxidizepropylene stably with molecular oxygen in a vapor phase to stablyproduce acrolein and acrylic acid, and to catalytically oxidizeisobutylene or tert-butyl alcohol stably with molecular oxygen in avapor phase to stably produce methacrolein and methacrylic acid.

The vapor-phase catalytic oxidation reaction is usually carried out byfilling the catalyst of the present invention in a fixed bedmultitubular reactor and feeding a raw material gas containing a rawmaterial compound selected from the group consisting of propylene,isobutylene and tert-butyl alcohol, and molecular oxygen. An air isusually used as a source of molecular oxygen. Besides the raw materialcompounds and molecular oxygen, the raw material gas may optionallycontain nitrogen, carbon dioxide, carbon monoxide, water vapor and thelike.

The reaction temperature is usually from 250 to 400° C. The reactionpressure may be reduced pressure, but it is usually from 100 to 500 kPa.The amount of molecular oxygen is usually from 1 to 3 moles per mole ofthe raw material compound. The space velocity (SV) of the raw materialgas is usually from 500 to 5000/h at STP (standard temperature andpressure, such as a temperature of 0° C. and a pressure of 100 kPa).

Examples of the present invention are shown below, but they do not limitthe present invention in any way. In the examples, the unit “ml/min”indicating the flow rate of gas is at STP, unless otherwise stated.

Falling Strength Test of Catalyst

A stainless steel mesh having 4.76 mm openings is fixed at the bottom ofa metal tube having an inner diameter of 30 mm and a length of 5 m andbeing arranged almost perpendicularly to the horizontal direction sothat the plane of the mesh is substantially horizontal. Then, X g of acatalyst is charged from the top of the metal tube to fall. The fallencatalyst particles are collected and placed on a sieve having 4.76 mmopenings, followed by vibration of the sieve. Then, Y g of the catalystparticles remain on the sieve. The falling strength (%) of the catalystis defined as follows:Falling strength(%)=Y/X×100(%)

In the Examples, a conversion (%) and a yield are defined as follows:Conversion(%)=100×[(moles of supplied isobutylene)−(moles of unreactedisobutylene)]/(moles of supplied isobutylene)Total yield(%)=100×(total moles of methacrolein and methacrylicacid)/(moles of supplied isobutylene)

EXAMPLE 1 (a) Preparation of Calcined Product [Step (1)]

13,241 g of ammonium molybdate [(NH₄)₆Mo₇O₂₄.4H₂O] was dissolved in15,000 g of warm water to form Liquid A. Separately, 6,060 g of iron(III) nitrate [Fe(NO₃)₃.9H₂O], 13,096 g of cobalt nitrate[Co(NO₃)₂.6H₂O] and 585 g of cesium nitrate [CsNO₃] were dissolved in6,000 g of warm water and subsequently 2,910 g of bismuth nitrate[Bi(NO₃)₃.5H₂O] was further dissolved to form Liquid B. Liquid B wasadded to Liquid A while stirring to form a slurry. The slurry was thendried with a flash dryer to obtain a dried product. Nine (9) parts byweight of silica alumina fiber (RFC400-SL produced by Saint-Gobain™) and2.5 parts by weight of antimony trioxide (Sb₂O₃) were added to 100 partsby weight of the dried material. The resulting mixture was molded into aring form having an outer diameter of 6.3 mm, an inner diameter of 2.5mm and a length of 6 mm, and then was calcined at 545° C. for 6 hours inan air flow to obtain a calcined product. This calcined productcontained 0.96 bismuth atom, 2.4 iron atoms, 7.2 cobalt atoms, 0.48cesium atom and 0.48 antimony atom per 12 molybdenum atoms.

(b) Reduction Treatment [Step (2)]

Seventy-five (75) ml of the calcined product obtained in the above step(a) was filled in a glass tube, and then a mixed gas ofhydrogen/nitrogen (5/95 by volume) was flowed at a flow rate of 300ml/min. through the glass tube to conduct a reduction treatment at 345°C. for 8 hours. Then, the supply of hydrogen was stopped, and theproduct was cooled to room temperature while flowing the nitrogen gasalone to obtain a reduced product. The mass loss due to the reductiontreatment was 1.04% by weight.

(c) Second Calcination [Step (3)]

The reduced product obtained in the above step (b) was calcined at 350°C. for 3 hours in an air flow to obtain Catalyst A.

(d) Falling Strength Test of Catalyst A

Thirty (30) g of Catalyst A obtained in the above step (c) was subjectedto the falling strength test described above. The falling strength ofCatalyst A was 91.8%. The result is shown in Table 1.

(e) Oxidation of Isobutylene

Into a glass reaction tube having an inner diameter of 18 mm, 14.3 ml ofCatalyst A obtained in the above step (c) was filled after being dilutedwith 30 g of silicon carbide (SHINANO-RUNDUM GC F16 produced by ShinanoElectric Refining Co., Ltd.). An oxidation reaction was conducted at areaction temperature of 360° C. by supplying a mixed gas ofisobutylene/oxygen/nitrogen/steam (1.0/2.0/10.0/2.7 by mole) into thereaction tube at a flow rate of 157.5 ml/min. The conversion ofisobutylene and the total yield of methacrolein and methacrylic acidwere 98.9% and 79.6%, respectively.

EXAMPLE 2 (a) Preparation of Catalyst [Steps (1), (2) and (3)]

Catalyst B was prepared in the same manner as in the steps (a), (b) and(c) of Example 1 except that the calcining temperature in the step (c)of Example 1 was changed from 350° C. to 370° C.

(b) Falling Strength Test of Catalyst B

Thirty (30) g of Catalyst B obtained in the previous step (a) of thisExample was subjected to the falling strength test described above. Thefalling strength of Catalyst B was 91.9%. The result is shown in Table1.

EXAMPLE 3 (a) Preparation of Calcined Product [Step (1)]

A calcined product was prepared in the same manner as in Step (a) ofExample 1 except that the amount of the silica alumina fiber was changedfrom 9 parts by weight to 12 parts by weight.

(b) Reducing Treatment [Step (2)]

A reduced product was prepared in the same manner as in Step (b) ofExample 1 except that the calcined product obtained in the previous step(a) of this Example was used in place of the calcined product obtainedin the step (a) of Example 1. The mass loss due the reduction treatmentwas 1.06% by weight.

(c) Second Calcination [Step (3)]

The second calcination was carried out in the same manner as in the step(c) of Example 1 except that the reduced product obtained in theprevious step (b) of this Example was used in place of the reducedproduct obtained in the step (b) of Example 1, the calcining temperaturewas changed from 350° C. to 330° C., and the calcining time was changedfrom 3 hours to 5 hours. Thereby, Catalyst C was obtained.

(d) Falling Strength Test of Catalyst C

Thirty (30) g of Catalyst C obtained in the previous step (c) of thisExample was subjected to the falling strength test described above. Thefalling strength of Catalyst C was 92.0%. The result is shown in Table1.

EXAMPLE 4 (a) Preparation of Catalyst [Steps (1), (2) and (3)]

Catalyst D was prepared in the same manner as in the steps (a), (b) and(c) of Example 3 except that the calcining temperature in the step (c)of Example 3 was changed from 330° C. to 420° C.

(b) Falling Strength Test of Catalyst D

Thirty (30) g of Catalyst D obtained in the previous step (a) of thisExample was subjected to the falling strength test described above. Thefalling strength of Catalyst D was 93.3%. The result is shown in Table1.

COMPARATIVE EXAMPLE 1 (a) Preparation of Catalyst [Step (1) Only]

The procedures of the step (a) of Example 1 were repeated to obtain acalcined product, which was used as Catalyst E.

(b) Falling Strength Test of Catalyst E

Thirty (30) g of Catalyst E obtained in the previous step (a) of thisComparative Example was subjected to the falling strength test describedabove. The falling strength of Catalyst E was 86.1%. The result is shownin Table 1.

(c) Oxidation of Isobutylene

Isobutylene was oxidized in the same manner as in the step (e) ofExample 1 except that Catalyst E obtained in the above step (a) of thisComparative Example was used in place of Catalyst A. The conversion ofisobutylene and the total yield of methacrolein and methacrylic acidwere 95.1% and 79.4%, respectively.

COMPARATIVE EXAMPLE 2 (a) Preparation of Catalyst [Steps (1) and (2)Only]

The procedures of the steps (a) and (b) of Example 1 were repeated toobtain a reduced product, which is referred to as Catalyst F.

(b) Falling Strength Test of Catalyst F

Thirty (30) g of Catalyst E obtained in the previous step (a) of thisComparative Example was subjected to the falling strength test describedabove. The falling strength of Catalyst F was 83.8%. The result is shownin Table 1.

COMPARATIVE EXAMPLE 3 (a) Preparation of Catalyst [Step (1) only]

The procedures of the step (a) of Example 3 were repeated to obtain acalcined product, which was used as Catalyst G.

(b) Falling Strength Test of Catalyst G

Thirty (30) g of Catalyst G obtained in the previous step (a) of thisComparative Example was subjected to the falling strength test describedabove. The falling strength of Catalyst G was 86.4%. The result is shownin Table 1.

COMPARATIVE EXAMPLE 4 (a) Preparation of Catalyst [Steps (1) and (2)Only]

The procedures of the steps (a) and (b) of Example 3 were repeated toobtain a reduced product, which was used as Catalyst H.

(b) Falling Strength Test of Catalyst H

Thirty (30) g of Catalyst H obtained in the previous step (a) of thisComparative Example was subjected to the falling strength test describedabove. The falling strength of Catalyst H was 84.6%. The result is shownin Table 1.

TABLE 1 Mass loss caused by Second reduction calcination Fallingtreatment Temp. Time strength Catalyst (wt. %) (° C.) (hrs) (%) Example1 A 1.04 350 3 91.8 Example 2 B 1.04 370 3 91.9 Example 3 C 1.06 330 592.0 Example 4 D 1.06 420 5 93.3 Comp. Ex. 1 E — — — 86.1 Comp. Ex. 2 F1.04 — — 83.8 Comp. Ex. 3 G — — — 86.4 Comp. Ex. 4 H 1.06 — — 84.6

What is claimed is:
 1. A method for producing an unsaturated aldehydeand/or an unsaturated carboxylic acid, comprising the steps of: (1)drying an aqueous solution or an aqueous slurry containing raw materialsof a catalyst and then calcining a dried product in a molecularoxygen-containing gas atmosphere to obtain a calcined product; (2)heating the calcined product obtained in Step (1) in the presence of areducing material to obtain a reduced product having a mass loss,represented by the following equation (I), of 0.05 to 6%:Mass loss (%)=[(Wa-Wb)/Wa]×100  (I) in which Wa is a weight of acalcined product before the reduction treatment, and Wb is a weight of areduced product after the reduction treatment; and (3) calcining thereduced product obtained in Step (2) in a molecular oxygen-containinggas atmosphere to obtain a catalyst comprising a mixed oxide comprisingmolybdenum, bismuth and iron, and (4) performing a gas phase catalyticoxidation of at least one compound selected from the group consisting ofpropylene, isobutylene and tertbutyl alcohol with molecular oxygen inthe presence of the catalyst produced in step (3).